The present invention is related to doppler detection from a radar return and, in particular, to the measurement of a single radar return instead of multiple returns to obtain doppler information. The invention is implemented with dispersive Surface Acoustic Wave (SAW) filters using tapered transducers.
U.S. Pat. No. 4,635,008, issued Jan. 6, 1987, entitled "Dispersive SAW Filter with Tapered Transducers," which was invented by the inventor of the present invention and is assigned to the assignee of the present invention, describes a unique single array dispersive SAW filter. This SAW filter employs input and output transducers which are aligned with respect to the array so that the angle of incidence of a SAW from the input transducer is approximately equal to the angle of reflection from the reflective array, over the entire frequency range of the dispersive array. The input and output transducers are constructed to provide a wide band frequency response which is matched to the periodicity of the dispersive array. In the preferred embodiment of the design, the transducers are formed with hyperbolically curved electrode fingers.
The dispersive SAW filter of U.S. Pat. No. 4,635,008 may be implemented as either an "up-chirp" or a "down-chirp" filter. When an up-chirp filter is implemented, the filter provides a rising time delay versus frequency characteristic, whereby high frequencies are delayed for a greater period of time than are low frequencies. If the time delay decreases as the frequency of the applied signal increases, the filter is a down-chirp filter.